Thermionic gas-filled rectifier circuit



Patented July 8, 1947 THERMIONI C GAS-FILLED RECTIFIER CIRCUIT HenryThomas Ramsay, Hatch End, England, assignor to The M-O Valve CompanyLimited,

London, England Application November 23, 1942, Serial No. 466,651 InGreat Britain November 5, 1941 This invention relates to circuitarrangements comprising a thermionic gas-filled rectifier of gridcontrol type wherein the thermionic cathode is separated from the anodeby a labyrinth, and a control electrode separate from the cathode andthe anode, wherein the main discharge between cathode and anode fromlines L, L is started by making the control electrode so much positiveto the cathode that a subsidiary discharge passes between thoseelectrodes, and produces ions in such a position and in such an amountthat they enable the main discharge to start between the cathode andanode.

It is important to distinguish circuit arrangements of this type fromthose wherein the rectifier is of the kind in which the function of thegrid is substantially the same as that of the control grid in a vacuumtriode, namely to co-operate with the anode in establishing at thesurface of the thermionic cathode a field sufficiently great to permit alarge proportion of the electrons emitted from the cathode to leave theneighbourhood of the cathode. Accordingly the foregoing description ofmy improved type will be explained further.

The term labyrinth is defined as a baffle or shield arrangement suchthat the starting of an ion-forming discharge from the cathode issubstantially independent of the potential difference between anode andcathode. A necessary condition for such independence is that no straightline can be drawn from anode to cathode that does not intersect aconductor that is negative to the anode during the starting period. Astraight line passing through an aperture in a grid is not to be held tointersect the grid. But this condition is not sufiicient. A sufiicientcondition alone is that, if the anode and cathode potential is heldconstant and the control electrode is made progressively more positiveto the cathode, the potential of the control electrode at which anion-forming discharge first occurs (evidenced by a very sharp rise inthe current between control electrode and cathode) is substantiallyindependent of the anode-cathode potential. This proves that the anodeand control grid do not co-operate in the starting of the firstion-forming discharge. The anode potential is efiective only inconverting this first discharge into a discharge between anode andcathode in virtue of the introduction of ions into the labyrinth.

It may be noted also that the two types difier greatly in the power thathas to be supplied in operation to the control electrode. In the type 7Claims. (Cl. 315261) in which the control grid operates as the controlgrid of a vacuum triode, the power has to be sufficient only to raisethe potential of the control grid; it is determined by the capacities Iof the electrodes and is generally of the order of a milliwatt. In thetype to which the invention relates the power supplied has to besufficient to provide an ion-forming discharge and generally is of theorder of a watt. In circuit arrangements of the type specified theremust be eificient deionisation of the labyrinth in the interval betweentwo main discharges. An ob ject of this invention is to provide incircuit arrangements of this type means for promoting such deionisation.

The electrode that is bombarded by positive ions during the deionisationperiod will sputter to some extent. Any sputtered matter that reachesthe thermionic cathode will tend to impair its eificiency. The life ofthe cathode may be maintained at a reasonable value by limiting thenegative potential imposed on the bombarded electrode or the positiveions flowing to it, and thus limiting the sputtering. But then thedeionising effect of that electrode is also limited. A further object ofthe invention is to provide means for preventing much of the sputteredmaterial from reaching the cathode.

Another object of this invention is to provide improved gas-filledthermionic rectifiers capable of use in the improved circuitarrangements.

Further objects and advantages of the invention will be apparent fromthe following description of three embodiments thereof, given by way ofexample with reference to the accompanying drawings, in which:

Figures 1 and 2 show respectively the relevant 5 parts of two difierentrectifiers in axial section, together with certain circuit elementsrepresented diagrammatically, and

Figure 3 shows a modified circuit arrangement capable of use with therectifier shown in Figure 2.

In the rectifier shown in Figure 1, the same structure serves both asthe control electrode and as the auxiliary electrode that operates towithdraw positive ions from the labyrinth, I is the thermionic cathode,2 the anode, 3 is a tubular or cup-shaped metal shield surrounding thecathode and connected to the cathode. The auxiliary or control electrodeis made up of a tubular electrostatic shield member 4 round the anode, ametal tube 6, and a control member or plate 5 spaced from and coveringthe end of the tube 6 within the tubular shield 4; the parts 4, 5, 6 areelectrically connected, and are maintained normally negative to thecathode by a bias source of E. M. F. 1 acting through a choke 8 and alead l3. The plate acts as a bafiie and is the main operative element ofthe labyrinth forcing the electrons to, follow a circuitous path intraveling from cathode to anode. These parts shield the cathodecompletely from the potential of the anode. The current to be rectifiedis, of course, applied to the lead lines L, L.

To start the discharge, a pulse of positive potential, generated from asource 9 of any of the mechanical or electronic types well. known in theart, is applied to the auxiliary electrode through a resistor I 9; thechoke 8 prevents the shortcircuiting of the pulse through the battery.An ion-forming discharge is thus started between the cathode and theauxiliary electrode, the current being limited by the resistor in. Theions produced by this discharge are within the potential field of theanode 2 and enable the main discharge to flow from the anode around theedge of the control plate 5 and through the electrostatic shield by wayof the tube 6. When the discharge has been extinguished by reduction ofthe alteri nating potential being rectified, the timing is such that thepulse is removed and the auxiliary electrode is therefore negative andcollects the residual positive ions. There is nothing to prevent mattersputtered from the parts 5 and 6 in Fig. 1 from reaching the cathode;consequently it will be understood that the negative potential at whichthey may be maintained is limited.

In Figure 2, the numerals I, 2, 3, 4, 5, I, 8, 9 represent partscorresponding to those. similarly denoted in Figure 1; but there is notube 6 projecting into the tubular member 3. On the under side of theplate 5 is a plate II insulated from it. This plate II, which serves asa baffle, i connected to. the. tubular shield 4 by a resistor [2 to apoint on which, intermediate between its ends, the pulse generator Sisconnected.

The discharge is started as before by a. pulse from 9 making 4, 5 and.II all positive. The ions produced in the vicinity of the electrode IIare within the potential field of anode 2 and therefore the maindischarge between anode 2 and cathode l starts. When the main dischargeis extinguished by reduction ofthe potential being, rectified, the fulldeionising current can flow. to the negative tubular shield 4 and theplate 5; but material sputtered from them is prevented from reaching thecathode by the baffle plate II. On the other hand the baffle plate IIhas the. resistance l2 in series with it, and the deionising current toit is limited so that there is no objectionable amount of sputteringfromions landing on it. Of course the deionisation is lessrapid inside thetubular heat shield 3 than inside the tubular shield 4; but so long asdeionisation is sufiicient, somewhere in the path through the labyrinthbetween anode and cathode the desired result is achieved.

Figure 3 shows a modification of the circuit of Figure 2. In thismodification the partsd, 5 are always negative; the positive pulse isapplied by the pulse generator 9to the plate I I, which acts as thecontrol electrode, through the resistor [2A. In thisarrangement morepower has to. be supp ied. by he nerato 9 n der to s ar the discharge.

I c aim:

1. In rectifier circuits, a gas tube having. an. anode, a cathode, anauxiliary electrode and a.

tubular metal cylinder surrounding said auxiliary electrode, saidauxiliary electrode and cylinder being positioned between the cathodeand anode and adapted to screen the cathode completely from the anodepotential, means for applying a sufficiently low voltage between thesaidauxiliary electrode and said cathode to prevent flow of electronsfrom the cathode to the auxiliary electrode and means for applying anintermittent positive voltage across said auxiliary electrode andcathode sufiicient to produce a flow of electrons from the cathodethereto.

2. In rectifier circuits, a gas tube having an anode, a cathode, animperforate control electrode and a tubular metal cylinder surroundingand spaced from said control electrode, said control electrode andcylinder being positioned between the cathode and anode and adapted toscreen the cathode completely from the anode potential, means forapplying a negative bias voltage between the said control electrode andsaid cathode to prevent flow of electrons from the,

cathode to the control electrode and means for applying an intermittentpositive voltage across said control electrode and cathode sufficient toproduce a flow of electrons from the cathode thereto;

3. In rectifier circuits, a gas tube having an anode, a cathode, animperforate control electrode and a tubular metal cylinder surroundingand spaced from said control electrode having a fiange projectinginwardly under said control electrode, said control electrode andcylinder being positioned between the cathode and anode and adapted toscreen the cathode completely from the anode potential, means forapplying a negative bias voltage between the said control electrode andsaid cathode to prevent flow of electrons from the cathode to thecontrol electrode and means for applying an intermittent positiveVoltage across said control electrode and cathode suificient to producea flow of electrons from the cathode thereto.

4. In rectifier circuits, a gas tube hav ng. an

' anode, a cathode, an imperforate control electrode and a tubular metalcylinder positioned between said cathode and anode and adapted to.

shield thepotentialof the anode completely from said cathode andincompletely from the space.

adjacent the control electrode, whereby the anode potential exerts noforce on the, electrons adjacent the cathode and a substantial forceonthe electrons adjacent said control; electrode, means for biasing saidcontrol electrode negative to said cathode and means for applying anintermittent positive voltage acrosssaid control elec-.

trode and cathode sufiicient to produce a momentary flow of electrons tosaid control electrode ,for ionizing the space adjacent thereto by.collision with gas atoms to start a discharge between the anode andcathode.

5.. In rectifier circuits, a gas tube having. an anode, a cathode, animperforate control, electrode, a tubular metal cylinder around andspaced from the control electrode, a second metal cylinder of lesserdiameter than the control electrode and spaced therefrom, said controlelectrode and cylinders shielding the potential of the anode completelyfrom said cathode and incom- "pletely from the space around the controlelectrode, whereby the anode potential exerts .substantially no forceonthe electrons adjacent the cathode and a substantial force on theelectrons adjacent said control electrode, means for biasing saidcontrol electrode negative to said cathode and means for applying apositive voltage pulse across said control electrode and cathodesulficient to produce a momentary flow of electrons to said controlelectrode for ionizing the space adjacent thereto and thereby startingthe discharge between the anode and cathode.

6. In rectifier circuits, a gas tube having an anode, a. cathode, twoimperforate and insulated electrodes between the cathode and anodebarring direct electron travel between the cathode and anode, a metalcylinder around and spaced from said imperforate electrodes, saidcylinder having a flange projecting between the cathode and theimperforate electrodes, an impedance connected between said imperforateelectrodes, means for applying a negative bias voltage between oneterminal of said impedance and said cathode, and a positivepulse-forming device connected between the cathode and an intermediatepoint in said impedance.

7. In rectifier circuits, a gas tube having an anode, a cathode, twoimperforat-e and insulated electrodes between the cathode and anodebarring direct electron travel between the cathode 6 and anode, a metalcylinder around and spaced from said imperforate electrodes, saidcylinder having a flange projecting between the cathode and theimperforate electrodes, a resistance connected between said imperforateelectrodes, means for applying a negative bias voltage between oneterminal of said resistance and said cathode, and a positivepulse-forming device connected between the cathode and an intermediatepoint in said resistance.

HENRY THOMAS RAMSAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,227,829 I-Iansell Jan. 7, 19412,145,088 Kobel Jan. 24, 1939 2,113,392 Baruch Apr. 5, 1938 2,100,196Lowry Nov. 23, 1937 1,702,785 Leblanc Feb. 19, 1929

